The need for rigid protective inserts in footwear products has long been recognized. Footwear products, particularly rubber boots, are often used in hazardous environments where sharp objects can puncture the footwear product and injure the wearer. For example, firemen wear rubber boots on the job. Sharp objects, such as upturned nails protruding from boards on the ground or floor, can puncture the boot and cause injury unless a rigid protective insert are used to prevent penetration of the sharp object. For this purpose, currently available fireman's safety boots contain a metal midsole insert having the same shape as the sole of the foot.
Various other protective inserts are used in footwear products both to protect the wearer from injury and provide rigidity to the footwear product. Rubber footwear products, for example, have incorporated a heel support or heel counter which is embedded within the footwear product as described in commonly-assigned U.S. patent application Ser. No. 07/495,021. A rigid safety toe cap, likewise embedded within the layers of the boot, protects the wearer's toes.
As described in the above-cited U.S. patent application, rubber footwear products are conventionally made from uncured rubber or rubber-coated fabrics that are cut to a desired size for a specific part of the footwear product and then assembled on a forming device, such as a metal last. The uncured rubber assembly is vulcanized for about one to two hours at temperatures ranging from about 200 to 400 degrees fahrenheit. This vulcanization chemically and physically melds the component parts by cross-linking the uncured rubber into a complete vulcanizate footwear product so that the resulting footwear product has a unitary construction. Cross-linking occurs both within the individual assembled component parts and between each part. Throughout this application, this melding of component parts will be referred to as "intervulcanization". Multilayer rubber boots of this type are generally described in Barma U.S. Pat. Nos. 4,703,533 and 4,858,337.
This conventional formation of rubber footwear products, relying on intervulcanization of the component parts, places severe constraints on the type of rubber footwear which can be produced. Conventional rubber footwear is flexible and does not provide rigid support or protection common in other kinds of footwear. However, the vulcanization process provides a product resistant to air, gas, sunlight, hydrocarbons, moisture penetration, fats and oils, acid and other chemicals, as well as providing a product having excellent durability, wear, and strength. It is desirable to maintain these attributes while providing a footwear product which protects the wearer from the penetration of sharp objects.
Known safety boot designs fail to recognize that placing a rigid steel plate in the sole of the boot does not completely protect the foot from sharp objects. An inside portion of the human instep near the sole remains unprotected by a midsole insert. The present invention provides more complete protection by providing a rubber footwear product with a rigid protective insert that protects the sole of the wearer's foot and also the inside or arched portion of the wearer's instep that is exposed to penetration by sharp objects from below.